Your network as clock-watcher
Network time synchronization is an important part of network design and
implementation. You need a time-synchronized network for healthy operation of
network operating systems and applications; synchronization is critical for
businesses that depend on a computer network. For example, many network
directory services systems exchange information and synchronize changes in the
directory services database according to time stamps. Groupware applications
require accurate time for scheduling and collaboration. Without a
time-synchronized network, time-sensitive systems and applications will not work
correctly. In a Windows NT network, all NT servers and client workstations need
to synchronize with a single, accurate, and standard time source.
Although Microsoft doesn't supply a built-in time service in NT, the Microsoft
Windows NT Resource Kit CD-ROMs for NT 3.51 and 4.0 provide a TimeServ
utility. TimeServ is an NT service that can synchronize the system time with a
time source either on the network or from outside. Microsoft also provides a
network command, NET TIME, that synchronizes a computer on a Microsoft network
with network time. This article introduces the two Microsoft time
synchronization utilities, outlines how to design a time-synchronized NT
network, and guides you in configuring and implementing time synchronization.
Windows NT Time Service
TimeServ works with NT Server and NT Workstation 3.5, 3.51, and 4.0. Because
TimeServ is an NT service, it runs in the background even when no one is logged
on the system. TimeServ keeps an NT computer synchronized with standard time
from a remote site or on the network. Components of time synchronization are
standard time sources, master time servers, primary time servers, and secondary
time servers.
A remote time service provider is a standard time source.
Generally, it is a standard Greenwich Mean Time service provider, such as the
National Institute of Standards and Technology (NIST) in Boulder, Colorado, or
the US Naval Observatory (USNO) in Washington, D.C. You can obtain the standard
time using a modem or the Internet.
An NT server or workstation is called a master time server if it
obtains standard time from a remote standard time source or from a network time
server that supports Network Time Protocol (NTP) on IP. The master time server
then provides this standard time to the rest of the network. At least one master
time server must be on a time-synchronized network. For redundancy, two or more
master time servers can be on the same network. However, Microsoft recommends
that all master time servers use the same standard time source.
An NT server or workstation is a primary time server if it obtains
network time from a specific NT time server on the network. This server is
generally a master time server or an NT time server that provides good time
on the network. A server provides good time if its time drifts less than 0.5
second from system time. The time service records time drift in the Application
log of the Events Viewer when the time service sets the system time to network
time. If the time drifts more than 0.5 second, the server may need to obtain
time more frequently. Any number of primary time servers can be on the network.
An NT server or workstation is a secondary time server if it
obtains network time from a specific NT domain. This domain can be the same
domain in which the secondary time server resides, or a different domain, if no
time server is in the same domain. Typically, you configure at least one
primary time server to be the time source that answers time requests from the
secondary time server. In some cases, you can use a master time server or even a
secondary time server as a time source, too, although a secondary time server is
usually a client of a time source.
Multitiered Time Synchronization System
You can envision NT network time synchronization as a multitiered time
synchronization system. A master time server at the top of the system obtains
standard time from a remote standard time source and then provides this time to
the entire network. Primary time servers in the middle of the system obtain
network time from a master time server and then give this time to secondary time
servers and client workstations. Secondary time servers and client workstations
reside at the bottom of the system and get network time from a primary time
server. Secondary time servers and client workstations are network time clients.
Figure 1 shows this multitiered time synchronization system.
Microsoft Network Time Command
Another way to synchronize time on a network is with Microsoft's NET TIME
network command. NET TIME is a DOS command for computers running NT, Windows 95,
Windows for Workgroups, or DOS/Windows with Microsoft network client software.
When you execute the NET TIME command, the workstation sets its system to
network time by searching for a time source in the domain. If a time source is
not present, the workstation will obtain time from a domain controller. For an
NT computer, you can issue the command
NET TIME /DOMAIN:<domain_name> /SET /Y
to set the time to network time. For a non-NT computer, you can enter the
command
NET TIME /WORKGROUP:<domain_name> /SET /Y
A computer can also synchronize its time with a specific computer if you
enter the command
NET TIME \\<computer_name> /SET /Y
You must assign Change the system time to the user on the
workstation so that NET TIME can work.
NET TIME works well for workstations when you add it to an NT domain logon
script. When a workstation logs on to a domain, the workstation system time is
set to the network time. TimeServ is a better utility for NT servers, because it
runs in the background.